The long-term objective of this proposal is to achieve a detailed understanding of the coupling between pre-mRNA splicing and mRNA export. The protein Aly, which is recruited to mRNA during spliceosome assembly and specifically promotes the export of spliced mRNA, is likely to play a key role in linking splicing to mRNA export. Thus, a detailed understanding of this protein and its interactions with these two major nuclear machineries is essential for understanding gene expression. The first specific aim is to map the functional domains in Aly that are required for interactions with the spliceosome and the export machinery. The second specific aim is to determine how Aly is recruited to the mRNA during spliceosome assembly. Finally, the third specific aim is to determine how Aly is targeted to the export machinery. Together, the proposed studies should lead to important insights into the coupling between splicing and mRNA export as well as into the mechanism of mRNA export.